1. Field of the Invention.
The instant invention relates to fuel systems for turbojet engines, more particularly toward a method and device for preventing excessive self-heating of the fuel in such systems.
2. Brief Description of the Prior Art.
One of the major advantageous characteristics of a dual flow turbojet engine (particularly such dual flow engines with a high dilution rate) is their very low fuel consumption at high altitudes, particularly when idling. In those conditions the rotational speed of the engine is rather high. The fuel systems for such engines typically have a positive displacement pump driven by the engine to supply the fuel to the engine's combustion chambers. A regulating value and a return line or recirculating line usually connect the output line of the positive displacement pump to the inlet line to recirculate the fuel which is not required by the engine. The output of the positive displacement pump is, of course, designed to supply the maximum amount of fuel required by the engine during high speed and/or low altitude operations. For those reasons, the output of the positive displacement pump results in a rather significant amount of fuel being recirculated during the low speed operations at altitude.
The large amount of recirculated fuel during the low speed, high-altitude operations results in an excessive fuel temperature rise. Depending upon the conditions at which the aircraft operates, the temperature rise may exceed 100.degree. F.
One solution to this problem is set forth in French Pat. No. 2,232,956 in which the turbojet engine fuel system utilizes a variable displacement pump. In this system, the output of the pump is decreased as the engines demand for fuel is reduced. Although this system has basically proven successful, the complexity of the variable displacement pump has decreased the reliability of the system as compared to a standard, positive displacement pump having a constant displacement volume (such as a gear pump).